Background

Cancer refers to any malignant tumor. There are many types of cancers which can occur in nearly every organ.  The pattern of growth of cancer cells often resembles a twisted and distorted version of the tissue that is arising.  Before we proceed, there are a few basic terms which must be defined.

A tumor means a swelling or mass.   A tumor can be benign or malignant. 

Benign refers to a tumor which does not have the potential to spread beyond the organ it arises.

Malignant refers to a tumor which has the ability to spread or metastasize beyond the organ from which it arises.

Broadly speaking, cancers can be divided into four major categories. 

1. A carcinoma is a cancer which is derived from the lining cells, or epithelium, of an organ.  There are 4 major types of epithelium in the body (Glandular, squamous, transitional, and pseudostratified).   Some types are only found in a few select organs such as the lung (pseudostratified) or urinary bladder (transitional).  Carcinomas can arise from any of these epithelial types. For example, breast carcinoma is most commonly derived from the lining cells of the milk producing glands.  A carcinoma with a glandular growth pattern is an adenocarcinoma.  Common adenocarcinomas include prostate, colon, and breast.  A carcinoma with a growth pattern resembling the squamous lining cells is termed a squamous cell carcinoma.  Common squamous cell carcinomas are found in the esophagus and skin.  However, any of these organs may have either type of carcinoma arising from it, although these latter diagnoses are exceedingly rare.

2. A sarcoma is a cancer derived from the soft tissues of the body.  Soft tissues include the fat, muscle, nerves, and connective tissue support.  Although not usually soft, it also includes bone and cartilage.

3. A lymphoma is a cancer derived from the white blood cells that are present in the lymphoid tissues of the body.   These sites most commonly include the lymph nodes and spleen. However, lymhomas may arise from any organ and body site.

4. A melanoma is a cancer derived from melanocytes.  These are the pigment producing cells present in the skin.   A mole is a benign growth of melanocytes. 

There are times when cancer cells display such a distorted and grotesque growth, that a recognizable growth pattern such as a carcinoma or sarcoma cannot be given.  In these cases, the pathologist may diagnose the tumor as a poorly differentiated or undifferentiated malignancy.  In some of these cases, additional studies and special stains or immunohistochemistry may aid in the final diagnosis.

As our diagnostic capabilities advance, pathologists have identified earlier and earlier forms of cancer.  Some of these cancers are termed in situ, designating a stage of cancer development where the cancer has not spread its usual confines of the basement membrane.  An in situ cancer cannot metastasize.   In addition, there are precancerous conditions termed dysplasia which in some cases, have a higher risk of progressing to cancer. 

OUTLINE

Pathogenesis
Commonly Used Terms
Internet Links

PATHOGENESIS	CHARACTERIZATION
CLONALITY
Clonality of Combined Tumors A Molecular Genetic Study Jiaoti Huang, MD, PhD, Carmen Behrens, MD, Ignacio I. Wistuba, MD, Adi F. Gazdar, MD, and Jaishree Jagirdar, MD From the Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY (Dr Huang); the Hamon Center for Therapeutic Oncology Research, Southwestern Medical Center, Dallas, Tex (Drs Behrens, Wistuba, and Gazdar); and the Department of Pathology, University of Texas Health Science Center at San Antonio, San Antonio, Tex (Dr Jagirdar)	Arch Pathol Lab Med 2002;Vol. 126, No. 4, pp. 437–441. Abstract quote Context.—Tumors with mixed morphologic patterns (combined tumors) are sometimes encountered, and questions often arise regarding the mechanism of molecular pathogenesis of each component and their relationships. Objective.—To determine whether different components of combined tumors contain the same or different genetic alterations, thus providing evidence for their clonality. Materials and Methods.—Six combined tumors with 2 components (in each case, both components showed epithelial differentiation morphologically) were studied by microdissecting tumor cells from each morphologic area followed by loss of heterozygosity analysis. Results.—In 1 of the cases studied, the different morphologic areas contained different patterns of genetic alterations. In the remaining 5 cases, the different morphologic areas harbored identical genetic changes in the chromosome regions studied. The latter group, interestingly, included a colonic tumor with an area of tubulovillous adenoma and an area of neuroendocrine carcinoma, and 2 lung tumors with squamous carcinoma and small cell carcinoma components. Conclusions.—Our results suggest that in the majority of combined tumors, cells with different phenotypes share similar genotype and may arise from a single precursor cell. However, in a minority of these tumors, different areas may be derived from different precursor cells.

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Basic Principles of Disease
Learn the basic disease classifications of cancers, infections, and inflammation

Commonly Used Terms
This is a glossary of terms often found in a pathology report.

Diagnostic Process
Learn how a pathologist makes a diagnosis using a microscope

Surgical Pathology Report
Examine an actual biopsy report to understand what each section means

Special Stains
Understand the tools the pathologist utilizes to aid in the diagnosis

How Accurate is My Report?
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Got Path?
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Pathologists Who Make A Difference
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Last Updated 1/5/2004

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